1. Technical Field
This invention generally relates to semiconductor devices, and more specifically relates to power conservation in semiconductor devices.
2. Background Art
The proliferation of electronics in our modern world is in large part due to integrated circuit semiconductor devices. Integrated semiconductor devices are designed and used in almost every electronic device today. In many applications power consumption is a critical issue for several reasons. For example, in portable devices such as wireless telephones, battery life and battery size are primary design concerns. Consumers want the portable electronic device to run as long as possible using a single battery charge and also want the device, including the battery to be as small and portable as possible. Thus, it is strongly desirable to be able to decrease power consumption of the device such that battery life can be extended and/or the size of the battery decreased.
In other applications power consumption is critical because it is directly related to the amount of heat generated by a device. A semiconductor device that consumes more power will generate more heat. In applications where heat sensitivity is a critical factor, reducing the power consumption reduces the heat generated by the device.
To achieve low-power consumption, many portable systems have a "sleep mode" or "standby mode" that reduces power consumption during periods of inactivity. During these prior art sleep modes, portions of the system are shut down and other portions operate at a reduced clock frequency. Turning non-essential portions of the system "off" and having the remainder of the system operating at reduced clock frequency reduces the power consumption during inactivity. Then, when an input stimulus is detected, the clock frequency is brought back up to full-speed and previously off portions of the system are turned back on.
While these systems reduce power consumption during periods of inactivity, they also have several disadvantages. These disadvantages include a lag time between "sleep" and full functionality of the system. In particular, because during sleep mode a portion of the system is effectively turned off, the system cannot immediately respond with full functionality when needed. Instead, the system must turn on the portions turned off during sleep, and then load or unload any data needed to or from the previously off portions before full functionality of the system returns. This lag time needed to return from sleep to full functionality makes sleep mode unacceptable for systems that require instantaneous functionality when an input stimulus is encountered.
Therefore, there existed a need to provide reduced power consumption by reducing power consumption during inactivity while maintaining the ability to become instantly active with full functionality.